Method of providing a black layer on a metal object



June 20, 1967 H. PROVISOR 3,325,648

METHOD OF PROVIDING A BLACK LAYER ON A METAL OBJECT Filed April 25, 1963 sb-m-m' Alloy INVENTOR.

HENRI PROVISOR AGENT United States Patent 4 Claims. (Cl. 29-194 The invention relates to blackening of metal surfaces, for example the inner surface of a metal support for the emissive alkaline-earth oxide layer of indirectly heated oxide cathodes for use in electron tubes, which black surface is located opposite the outer surface of the insulating layer of the filament wire, from which it is separated by a narrow high-vacuum space.

It is known that due to the reaction of aluminium with metals such as nickel, molybdenum, iron or with an alloy of these metals, a grey-black intermetallic layer can be obtained.

This process requires a thermal treatment in vacuo, in a reducing atmosphere or a neutral atmosphere between 610 and 650 C. for 15 to 30 minutes. Experience has shown that for certain cases this heating produces an inadmissible reduction in rigidity, so that difficulties can occur when building the heater body into the cathode, while at a high temperature the black layer vanishes.

The invention relates to a novel method of blackening metal surfaces, for example the inner surface of the support for the emissive layer of a cathode, in which method said disadvantages are obviated. Particularly the heating time, required for the formation of a blackish layer of intermetallic compounds is reduced, while the black layer itself has a greater thermal resistivity. The new method consists in that a layer of a suspension of antimony oxide in a suitable liquid is applied to the metal surface to be blackened, which surface is heated for about minutes at a temperature of about 650 C. in a reducing atmosphere.

To this end the antimony oxide (Sb O or Sb O is suspended in water or in a suitable organic liquid and then applied in known manner to the metal surface; the body thus coated is then heated at about 600 C. or more in a reducing atmosphere. The released antimony reacts with the metal of the body and forms a blackish surface layer. The speed with which this black layer is obtained is ascribed to the easy reduction of the antimony oxide and to the great reactivity of the locally formed antimony. Preferably aluminum powder is added to the suspension.

Apart from the said metals nickel, molybdenum and iron, which permit a reaction for obtaining a black surface, kinds of steel, even stainless steel, are found to be suitable to this end, as well as aluminum.

The figure shown in the drawing illustrates the article produced by the invention.

The method according to the present invention may be carried out as follows:

A nickel support of an indirectly heated cathode is coated with a suspension of 20 gms of antimony oxide Sb 0 in 100 mls. of nitrocellulose solution. The assembly is heated at about 650 C. for 5 minutes.

The antimony oxide alone provided a violet-like blackening, while the surface layer obtained by the thermal reaction is thin. An addition of aluminum powder to the antimony oxide suspension prevents the occurrence of the violet-like reflections and yields more or less deepblack shades in accordance with the quantities of aluminum. Moreover, experience has shown that black layers obtained by means of mixtures of antimony oxide and aluminum have a much greater resistance to heat than layers obtained by the reactoin of antimony oxide alone with the metal of the support. It has particularly been found that the surface of a nickel support, subsequent to blackening by means of a mixture of antimony oxide and aluminum remains black after a treatment at 800 C. for 500 hours in vacuo, whereas the surface of such a support, subsequent to blackening with only antimony oxide, becomes blank at said temperature in vacuo after a few hours.

A suitable suspension of aluminum powder and antimony oxide (Sb O may be composed in the following manner: 2.50 gms. of nitrocellulose is dissolved in gms. of glycol ethylene and 22.5 gms. of butanol; in mls. of this solution is suspended 20 gms. of fine aluminum powder and 10 gms. of antimony oxide (Sb O The presence of aluminum powder in the antimony oxide suspension practically does not affect the application of the method according to the invention. This may be accounted for by the fact that the antimony forms intermetallic compounds not only with the metal of the support but also with the aluminum powder.

This method, as described for the manufacture of indirectly heated oxide cathodes, may be employed substantially without any modification, in numerous other cases and will be successful with all surfaces which are heated in some way or other, and of which the heat absorption or the heat dissipation by radiation must be improved. This is the case, for example, with external surfaces of spaces provided with cooling vanes, with motors or heat exchangers. This method may also be used for obtaining certain decorative effects, particularly for trinkets or for protection from corrosion of iron or steel structures.

What is claimed is:

1. A method of blackening surfaces of metal bodies comprising the steps of applying a layer of a suspension of antimony oxide in a suitable liquid to the metal surface to the blackened and heating said liquid for about 5 minutes at a temperature of about 650 C. in a reducing atmosphere.

2. A method as claimed in claim 1, wherein aluminum powder is added to the antimony oxide suspension.

3. An object having a blackened surface portion comprising a metal base of a metal selected from the group consisting of nickel, molybdenum, iron and alloys thereof having a layer thereon of an intermetallic compound of antimony and said base metal.

4. A support for an electron emissive layer comprising a nickel base and a black layer of an intermetallic compound of antimony, aluminum and nickel on the side of said base remote from the electron emissive layer.

References Cited UNITED STATES PATENTS 2,710,253 6/1955 Willardson et al. 75149 2,816,023 12/1957 Genser et a1 75-149 FOREiGN PATENTS 478,754 4/1930 Germany. 932,858 9/ 1955 Germany.

ALFRED L. LEAVITT, Primary Examiner.

WILLIAM L. JARVIS, RALPH S. KENDALL,

Examiners. 

4. A SUPPORT FOR AN ELECTRON EMISSIVE LAYER COMPRISING A NICKEL BASE AND A BLACK LAYER OF AN INTERMETALLIC COMPOUND OF ANTIMONY, ALUMINUM AND NICKEL ON THE SIDE OF SAID BASE REMOTE FROM THE ELECTRON EMISSIVE LAYER. 